In the field of forest fire control one colloquially uses the term "portable water pump" to refer to a fluid displacement unit. For the purpose of clear presentation of the subject matter of this application the term "fluid displacement-unit" will be used instead of the general term "water pump" and kept distinct from a "fluid pump": a fluid displacement unit is an integral component adapted to convey water, the fluid displacement unit for forest fire control typically comprises a combustion engine driving a fluid pump.
In fire fighting, fluid displacement units are designed to operate unattended. The fluid displacement units typically convey water from a water store such as a lake. A fluid displacement unit conveys water from an input port such as a hose inserted in the lake to an output port such as a nozzle at and end of another hose. Operating characteristics of fluid displacement units are well established when the water supply at the input port is unlimited.
Water sources for forest fire fighting are sometimes limited in volume and when the water source is used up the fluid displacement units run dry. The closest water store to a forest fire is sometimes a slough or other limited store of water. Often the water in the water store is exhausted before the fire is put out or the fluid displacement unit is shut off. Typical operating characteristics of a fluid displacement unit when insufficient water is available to be drawn at the input port cannot be sustained for long periods of time without resulting damage to the fluid displacement unit.
The fluid pump and the combustion engine are designed to operate under load. Under load, water is conveyed through the fluid displacement unit. When insufficient water is available at the input port the load is decreased for the same torque provided by the combustion engine. The result is that the fluid pump develops a greater rotational speed and in turn the combustion engine tends to run at a higher speed. Higher running speeds induce heating in the mechanical components of the fluid pump and/or the combustion engine. Excessively high running speeds lead to excessive heating. Excessive heating results to damage to the parts of the fluid displacement unit by seizing either the fluid pump or the combustion engine.
It is known in the art to control rotational speed of combustion engines. There are numerous teachings of speed control enabling combustion engines to run at a predefined speed. These methods are unsuited for conveying of water since typically the cooling effects of the conveyed water onto the components of the fluid pump are taken into account in the design of fluid displacement units to minimize the production costs therefore leading to excessive heating when running dry. Other teachings call for operational speed monitoring and control allowing the fluid displacement unit to run at a lower idling speed when the water supply is insufficient at the intake port. Both of the above mentioned teachings are unsuited for the operation of a portable fluid displacement unit for forest fire control purposes since more often than not fuel resources are also limited and when water is not being pumped it is preferable that fuel resources be conserved. Current field practice utilizes methods of shutting off the combustion engine when the water supply is insufficient at the intake port.
Typically shutting off the engine involves a latching component which trips when an over speed condition in effect is sensed. To date, these latching components employ mechanical latching techniques and necessitate manual reset prior to restarting the combustion engine. More often than not ignorant and rookie/frustrated forest fire fighters omit resetting the latch and endlessly attempting to restart the combustion engine, often leading to flooding of the engine. Other rookie/frustrated fire fighters aware of the latching component block the action of the latching component in a position enabling operation of the fluid displacement unit under normal conditions but defeating the purpose of this protection against damage to the fluid displacement unit running at high speeds due to an insufficient supply of water at the intake port.
There is therefore a need for an apparatus and method for automatic shut-off of a combustion engine driving a fluid pump of a fluid displacement unit to protect the fluid displacement unit form damage and to automatically reset the combustion engine for manual restart subsequent to the combustion engine spinning down to a rest.